Composite materials have well-documented advantages over traditional construction materials, particularly in providing excellent mechanical properties at very low material densities. As a result, the use of such materials is becoming increasingly widespread and their application ranges from “industrial” and “sports and leisure” to high performance aerospace components.
Prepregs, comprising a fibre arrangement impregnated with resin such as epoxy resin, are widely used in the generation of such composite materials. Typically a number of plies of such prepregs are “laid-up” as desired and the resulting laminate is cured, typically by exposure to elevated temperatures, to produce a cured composite laminate.
One hazard associated with such a process is the entrapment of gas between the layers of prepreg which results in undesirable porosity in the cured composite laminate. Porosity has a negative impact on the mechanical properties of the cured composite laminate and is therefore ideally minimised or eliminated.
It is known that the application of pressure during the curing process can reduce the final porosity of the cured laminate. If a low porosity composite is desired, e.g. for demanding applications such as aerospace, then prolonged exposure to high temperature and pressure, e.g. by curing the laminate in an autoclave, is the only practical option. However, the application of high pressure and temperature for prolonged periods is costly and slow.
Curing methods which involve lower pressures, e.g. the known vacuum bag process, are cheaper and quicker alternatives but usually result in higher porosity in the cured laminate.
Consequently, efforts have been made to reduce porosity by adapting the structure of laminates before curing.
U.S. Pat. No. 5,104,718 discloses a laminate of prepregs wherein the prepregs have longitudinal grooves parallel to the unidirectional fibres within the prepregs.